1. Field of the Invention
The present invention relates to a camera system which is arranged to perform light measurement by performing a preliminary emission before a main emission for photography and compute a control value optimum for the main emission.
2. Description of the Related Art
In a conventional type of camera system which is arranged to determine whether correct exposure of a subject is possible, on the basis of the result of light measurement using preliminary emission, invisible light is projected toward the subject as a preliminary emission and, if correct flash exposure is expected on the basis of the subject-reflected light, a predetermined display mark is continuously lit to provide a display indicating that flash control is possible. If incorrect flash exposure is expected, the predetermined display mark is blinked to provide a warning display.
It is also known that, in a conventional TTL flash control type of camera system, if emission stop control of a flash unit is carried out within a predetermined time, it is determined that correct flash control has been performed.
However, the former type of camera system has the following problem. If a preliminary emission is performed while a capacitor for storing energy to be used for emission of a flash unit is being charged, it is possible to determine whether flash control is possible at the time of the preliminary emission, but if a preliminary emission is performed with flash control being impossible and the capacitor is subsequently charged up to a higher voltage, it is impossible to determine whether flash control has become possible as the result of the voltage rise of the capacitor.
The latter TTL flash control type of camera system has the problem that a difference in emission stop time occurs owing to the differences in reflectance between various kinds of films, so that no accurate decision result can be obtained.
Japanese Laid-Open Patent Application Nos. Sho 61-156239 and Sho 61-156240 propose other types of camera systems. In these camera systems, prior to photography, a preliminary emission pointed at a subject is carried out and the light reflected from the subject is received, and a control value for a main emission for photography is determined as a relative amount of the amount of the received light. During photography, if the actual amount of emission of the main emission reaches the determined amount of emission, the main emission is made to stop, so that a correct amount of main emission can be achieved.
Some types of camera systems which are provided with flash units employ an automatic zoom flash system which can vary the illuminating area of a flash unit by automatically changing the illuminating angle or the like of the flash unit according to the focal length (zooming) of a photographing lens. Such an automatic zoom flash system is also employed in the aforesaid type of camera system which performs preliminary emission and main emission.
Japanese Laid-open Patent Application No. Sho 60-61733 proposes a camera system which is arranged to warn a photographer if the illuminating area of a flash unit is varied after a preliminary emission. Japanese Laid-open Patent Application No. Sho 60-100125 proposes a camera system which is arranged to again perform a preliminary emission if the illuminating area of a flash unit is varied after a preliminary emission. However, the former camera system which only issues a warning cannot meet the demand for automation of photography. The latter camera system which again performs a preliminary emission after a preliminary emission has the problem that not only is a person who is a subject dazzled by the repetition of preliminary emissions but also emission energy is wastefully consumed.
Another conventional type of automatic exposure camera system is capable of performing control called "AE lock", i.e., the control of memorizing and fixing a measured light value of ambient light at an arbitrary point in time. For example, if a photographer desires to take a picture in which a main subject is located on one side of an image plane against the bright sky under a backlight condition, as shown in FIG. 36, the photographer first carries out AE lock with the camera system pointed at the main subject, as shown by a frame "a", and then moves the camera system so that the desired scene shown by a frame "b" can be photographed. In this manner, although the main subject is not located in the center of the image plane, the main subject can be photographed at a correct exposure level.
However, in the case of such a conventional automatic exposure camera system in which AE lock does not work during flash photography, if the scene shown by the frame "b" in which the main subject is not located in the center of the image plane is photographed by flash photography with the camera system pointed at the scene shown by the frame "b" in FIG. 37, flash control is performed on the background, so that the main subject is photographed at a complete overexposure level.
To solve this problem, the aforementioned camera systems described in Japanese Laid-Open Patent Application Nos. Sho 61-156239, Sho 61-156240 and Sho 60-61733 have a so-called FE lock function. In this FE lock function, prior to photography, a preliminary emission, which is pointed at the main subject as shown by the frame "a" in FIG. 37, is carried out and the light reflected from the main subject is received, and a control value for a main emission for photography is determined as a relative amount of the amount of the received light. Then, if the camera system is pointed at the scene shown by the frame "b" and the main emission is performed by the determined amount of emission, the main subject can be photographed at a correct exposure level.
Some types of camera systems which are provided with flash units are arranged to be able to vary the illuminating area of a flash unit by changing the illuminating angle or the like of the flash unit according to the focal length (zooming) of a photographing lens. Such a flash unit is also employed in the aforesaid type of camera system having the FE lock function.